ALPs at Colliders

TL;DR

This work analyzes axion-like particles (ALPs) within a model-independent effective framework focusing on their couplings to photons ($g_{aγ}$) and gluons ($g_{ag}$). It derives collider bounds from mono-photon, tri-photon, and monojet searches at the LHC (7–8 TeV with projections to 13 TeV) and evaluates future $e^+e^-$ colliders, highlighting complementary sensitivity to heavier ALPs beyond astrophysical limits. The study combines channels to obtain model-dependent correlations (PQWW, KSVZ, DFSZ) and discusses the validity of the effective description, showing that monojet data can indirectly constrain $g_{aγ}$ under certain UV completions. It also proposes enhanced search strategies, including displaced-vertex and boosted-photon signatures, to maximize collider sensitivity and emphasize the role of colliders in closing gaps unexplored by helioscopes and beam-dump experiments.

Abstract

New pseudo-scalars, often called axion-like particles (ALPs), abound in model-building and are often associated with the breaking of a new symmetry. Traditional searches and indirect bounds are limited to light axions, typically in or below the KeV range for ALPs coupled to photons. We present collider bounds on ALPs from mono-$γ$, tri-$γ$ and mono-jet searches in a model independent fashion, as well as the prospects for the LHC and future machines. We find that they are complementary to existing searches, as they are sensitive to heavier ALPs and have the capability to cover an otherwise inaccessible region of parameter space. We also show that, assuming certain model dependent correlations between the ALP coupling to photons and gluons as well as considering the validity of the effective description of ALP interactions, mono-jet searches are in fact more suitable and effective in indirectly constraining ALP scenarios.

Figures (5)

• Figure 1: Feynamn diagram for ALP production in association with a photon giving rise to the mono-$\gamma$+$\slashed{E}_T$ signature.
• Figure 2: Current and prospective limits on ALPs in the ($M_{a}$, $g_{a\gamma}$) plane. Shaded areas represent existing experimental limits while lines denote the projected sensitivity of furture experiments.
• Figure 3: Limits in the ($M_{ax}$, $g^{g}_{ax}$) derived from the seven signal regions in the current CMS and ATLAS mono-jet analyses. Refer to Appendix \ref{['AppendixA']} for a definition of the selection processes and signal regions
• Figure 4: Left: Present limits on the coupling of ALPS to photons and gluons (purple area) along with correlations between the two couplings in different models (black lines and green band). Right: An illustration of the indirect limits on $g_{a\gamma}$ set by the monojet search assmuing the model dependent correlations.
• Figure 5: Ranges of effective cutoff derived from current and prospective limits on $g_{a\gamma}$ determined in this paper from tri-$\gamma$ searches, as shown in Fig \ref{['fig:ALP_gamma_limits']}. In the case of hadron colliders, the characteristic energy of each experiment is set either by $M_a$ or by the minimum $p_T$ requirement on the photons since the ALP is required to be produced nearly at rest. The scale of the $e^+e^-$ colliders is simply set by the centre of mass energy.